import java.util.ArrayList;
import java.util.List;

/**
 * \* Created with IntelliJ IDEA.
 * \* User: 冯若航
 * \* Date: 2021/5/24
 * \* Time: 18:58
 * \* To change this template use File | Settings | File Templates.
 * \* Description:
 * \
 */
public class Z字形变换 {
    public String convert(String s, int numRows){
        if(numRows<2){
            return s;
        }
        List<StringBuilder> rows=new ArrayList<>();
        for(int i=0;i<numRows;i++){
            rows.add(new StringBuilder());
        }

        int i=0,flag=-1;
        for(char c:s.toCharArray()){
            rows.get(i).append(c);
            if(i==0||i==numRows-1){
                flag=-flag;
            }
            i+=flag;
        }
        StringBuilder res=new StringBuilder();
        for(StringBuilder row:rows){
            res.append(row);
        }
        return res.toString();
    }
}